1. Field of the Invention
This invention generally relates to cardiology and, more particularly, to non-invasive and invasive cardio-electromagnetic therapy.
2. Description of the Background
Intrinsic rhythmicity is a well-established cardiac property. Intrinsic rhythmicity is the heart's ability to initiate its own heart rate, rhythm, and conductivity without nervous innervation. Even though the heart can initiate its own heart rate, rhythm, and conductivity, the autonomic nervous system is known to strongly influence heart rate, rhythm, and conductivity. The autonomic nervous system, in fact, has a great influence on other cardiac properties such as contractility (e.g., heart pump strength) and refractoriness (e.g., excitable readiness).
The autonomic nervous system has two components. One component, the parasympathetic nervous system, can cause slowing of the heart rate and slowing of atrio-ventricular (A-V) conduction in the heart. The A-V conduction rate is slowed when the parasympathetic nervous system releases acetylcholine at the atrio-ventricular node. The heart rate is slowed when the parasympathetic nervous system releases acetylcholine at the nerve terminals at the sino-atrial node. The sino-atrial node is considered the heart's primary “pacemaker.”
The other component of the autonomic nervous system is the sympathetic nervous system. The sympathetic nervous system, conversely, causes speeding of the heart rate, speeding of the A-V conduction rate, and constriction of blood vessels. The sympathetic nervous system releases neurotransmitters, such as epinephrine and norepinephrine, to speed heart rate and A-V conduction. The sympathetic nervous system is also known to cause an increase in the force of contraction of the heart muscle. The neurotransmitters epinephrine and norepinephrine have also been implicated in the irregular heart rhythm called arrhythmias. Arhythmias are irregularities of the heart rate arising from either the atria or the ventricles.
Because the autonomic nervous system is known to influence heart properties, research has focused on stimulating the autonomic nervous system. One research avenue shows that electrical stimulation of the autonomic nervous system causes the release of neurotransmitters. These neurotransmitters, as mentioned above, affect heart rate, rhythm, conductivity, and contractility. This electrical stimulation has, however, always required surgical dissection of the parasympathetic and sympathetic nerves. Surgical dissection of nerve tissue is not acceptable or practical for clinical studies and clinical purposes.
Another research avenue has been chemical stimulation. Researchers have chemically synthesized the neurotransmitters that affect heart rate, rhythm, conductivity, and contractility. This chemical stimulation has proven useful in modulating cardiac properties in clinical circumstances. “Beta-blockers” such as propanolol, for example, have been used as sympathetic nerve blocking agents. These beta-blockers have proven invaluable in controlling abnormalities of the heart's rhythm, rate, and conduction.
Chemical stimulation, however, is approached with caution. The effects of chemical stimulation are not completely understood. Chemically synthesized neurotransmitters, or similar agents, are very technologically new and the long-term effects are unknown. A further problem is that patients are often found to become non-compliant, i.e., they stop their medication or their compliance is irregular.
Accordingly, there is a need to stimulate the autonomic nervous system that does not require surgical dissection of nerve tissue, which is acceptable to clinical subjects, and is cost effective to administer. These advantages and other advantages are provided by the system and method described herein, and numerous disadvantages of existing techniques are avoided.